Effect of maternal metabolism on fetal growth and body composition.

The objective of this work is to examine the various maternal metabolic and parental anthropometric and demographic factors that affect fetal growth and body composition. These data are a review of previously published data evaluating 1) demographic and anthropometric factors associated with fetal growth; 2) differences in male and female neonatal body composition; 3) anthropometric and maternal metabolic factors correlated with neonatal birth weight, fat-free mass, and fat mass using stepwise logistic regression analysis; and 4) the relationship between maternal weight gain and birth weight in women with normal glucose tolerance (control subjects) and gestational diabetes mellitus (GDM). We estimated body composition in 186 neonates using anthropometry. Fat-free mass, which comprised 86% of mean birth weight, accounted for 83% of the variance in birth weight, and fat mass, which comprised only 14% of birth weight, accounted for 46% of the variance in birth weight. Male neonates were, on average, 175 g heavier than females. There was significantly (P = 0.0001) greater fat-free mass in males than in females but no significant difference in fat mass. Using stepwise logistic regression, we accounted for 29% of the variance in birth weight, 30% in fat-free mass, and 17% in fat mass. Independent variables included maternal height, pregravid weight, weight gain during pregnancy, education, parity, paternal height and weight, neonatal sex, and gestational age. Including maternal glucose insulin sensitivity in 16 additional subjects, we explained 48% of the variance in birth weight, 53% in fat-free mass, and 46% in fat mass. There was a positive (P = 0.0007) correlation between weight gain and birth weight in control subjects, but a negative (P = 0.34) correlation in women with GDM. In control subjects, the correlation was strongest in women who were lean before conception and became progressively weaker as pregravid weight for height increased. In women with GDM, there were no significant correlations between maternal weight gain and birth weight, irrespective of pregravid weight for height. The assessment of fetal/neonatal body composition may improve our understanding of the effect of differential factors on fetal growth. Factors associated with accretion of fetal adipose tissue in late gestation are less well understood in comparison with birth weight and fat-free mass. Additional studies of maternal glucose and lipid metabolism are needed to better evaluate fetal growth.